Why do onions make you cry?

Answer:

When you cut into an onion, a naturally occurring chemical irritant known as syn-propanethial-S-oxide is released into the air, which irritates our eyes, causing us to “tear” up. To reduce your tears while cutting onions, put them in the fridge for at least 30 minutes. Then, cut off the top and peel the outer layers leaving the root end intact.